Method and device for viewing a burner flame

ABSTRACT

A method of viewing the flame produced by a burner in a furnace in provided, comprising viewing the flame through an interference filter adapted to pass light of only a narrow wavelength range, in which the wavelength range corresponds to a wavelength which is stronger in the light emitted by the burner than in the ambient light of the furnace. The method is particularly applicable to viewing the flames produced by natural gas burners in petroleum crackers and the preferred wavelength range is that of sodium.

The present invention relates to a method and apparatus for viewing aflame in a furnace, such as for example a burner flame in the pyrolysissection of a petrochemical cracker reactor.

In a petroleum cracker, large hydrocarbon molecules such as ethane andpropane from natural gas, or heavier liquids such as naphta and gas oilfrom petroleum are split into smaller molecules. This is often done toprovide olefins such as ethylene that are useful in themselves, or maybe used in polymerisation processes.

In the case of ethane and propane, the gas is heated to above about 800°C. at which point bonds within the molecule break, producing a range ofsmaller molecules. The desired products are then separated out. The sameprinciple applies when cracking heavier substances, but since themolecules are much larger, a far greater range of smaller molecules isprovided. Although some processes provide a smaller yield of olefins,many other useful by-products are produced.

In a typical ethane cracker plant, the cracking takes place in apyrolysis section. Here, ethane is pumped through a maze of 100-150 mmdiameter tubes located within a furnace where it is heated up to about800° C. and cracks. The ethane never comes into direct contact with thesource of heat, if it were to do so it would ignite disastrously.

Typically, the pyrolysis section includes a plurality of burners whichare positioned adjacent the tubes through which the ethane is pumped.The burners combust a fuel such as natural gas in order to heat the gasin the tubes to the required temperature.

To achieve maximum thermal efficiency of the cracker the flame from eachof the burners should be maintained at the required size andorientation. This can be done by adjusting the quantity of fuel suppliedto the burner and/or by adjusting the ratio of fuel supplied to airand/or by adjusting the direction of the jets of fuel.

In order to monitor the size and orientation of the burner flames, anoperator views the flames at regular intervals and then makes anyadjustments which may be required. However, the heat in the pyrolysissection is such that the walls of the cracker are heated to atemperature of about 1100° C. Consequently, radiant beat is given offfrom the walls to create a bright background against which it is verydifficult to see the burner flames.

In the past, this problem has been overcome by adding either copper orsodium bicarbonate to the flames to provide a colour which is visibleagainst the bright background of the walls of the cracker. To do thishowever, the pyrolysis chamber must be opened up and the copper orsodium bicarbonate thrown into the flames. It will be appreciated thatat the operating temperatures in question this is a complex procedurewhich results in significant inconvenience and energy losses.

The present invention seeks to provide a method of viewing the flames ofthe burners in a furnace such as the pyrolysis chamber of a crackerwhich can be carried out quickly and easily and without the need to loseheat from the furnace.

The applicants have realised that if the light emitted by the burnerflames or a part of that light could be separated from the backgroundradiant light in the furnace, the burner flames could then be viewedwithout the need for complex solutions such as throwing additives intothe flames.

From a first aspect, the present invention provides a method of viewingthe flame produced by a burner in a furnace, wherein the fuel burnt bythe burner is natural gas, comprising viewing the flame through aninterference filter adapted to pass light of the wavelength of sodiumonly.

Thus, the interference filter acts to block out the bulk of the abientlight of the furnace such that the burner flame is clearly visible.

In one preferred embodiment of the invention, the furnace is thepyrolysis section of a petroleum cracker.

The method is particularly advantageous in such an environment as thewalls of the cracker are heated to a very high temperature such thatthey emit significant levels of white light which makes it difficult oreves impossible to see the flame of a burner in the cracker under normalcircumstances.

Typically, the fuel which is burnt in the petroleum cracker is naturalgas and most typically, a mixture of hydrogen, methane and air. Testshave shown that this fuel can contain traces of sodium. The reason forthis is not known but it is thought to be because methane and naturalgas often come from environments in which salt is present. In the methodof the invention therefore, the filter used is a sodium interferencefitter which filters out substantially all the light other than thesodium light emitted by the sodium trace elements in the fuel.

Preferably the sodium interference filter has a pass bandwidth ofapproximately 10 nm so that light of wavelength 0.584 to 0.594 μm maypass through the filter. More preferably the pass bandwidth is 2 to 5 nmand, still more preferably, the pass bandwidth is 1 nm so that onlylight of wavelength 0.589 μm passes through the filter.

The use of a sodium interference filter is particularly advantageous asthere is effectively no light of the wavelength of sodium present asambient light in the furnace such that the burner flame is very clearlyvisible using this method.

The sodium interference filter could take any form and the burner in thefurnace could be viewed through a door which is opened in use as inknown systems. Preferably however, a window is provided in the wall ofthe furnace through which the burner can be viewed. This has theadvantage that the furnace does not need to be opened each time that theburners are viewed. Thus the temperature inside the furnace is notdisturbed and thermal currents which can distort the action of theburner flame are not created by opening and closing the furnace atregular intervals.

Preferably, the window is made of quartz which is a material capable ofwithstanding the temperature gradient across the wall of the furnacewhile also providing the necessary transparency.

In one preferred embodiment, the interference filter could be providedas a panel attached to the window of the furnace.

Still more preferably, the filter in a panel which can be placed overthe window or removed by a user as required. Thus for example, thefilter could be hinged to the wall of the furnace to allow quick andeasy adjustment thereof.

In an alternative embodiment, a pair of glasses or goggles comprising aninterference filter in each lens thereof is provided. This has theadvantage of allowing a user to carry the glasses with him for examplefrom one furnace to the next. The goggles have the additional advantagethat they could also be used with a traditional furnace in which nosealed window is provided but a door is merely opened when a user wishesto look inside the furnace.

In a still further preferred embodiment of the invention, theinterference filter could be provided in a camera arranged inside thefurnace and adapted to photograph the burner at regular intervals. Theinformation from the camera could then be relayed to an operator whocould make any necessary adjustments to the burner from a remotelocation. This would clearly be advantageous in a large scale refineryor similar scale production plant where considerable numbers ofpersonnel would be required to monitor the operation of each furnace insitu.

Ideally the camera could be programmed to photograph the burner aboutonce every 10 minutes.

It will be appreciated that the furnace would normally include aplurality of burners and, in the case of a petroleum cracker, ten ormore burners could be provided. Thus if necessary, the camera could beprogrammed to move along a row of burners and to take several picturesof respective burners or groups thereof.

From a further aspect, the present invention provides an apparatuscomprising a furnace, a burner for burning natural gas in the furnaceand an apparatus for viewing the flame produced by the burner, theapparatus for viewing the flame comprising an interference filteradapted to pass light of the wavelength of sodium only.

In one preferred embodiment, the apparatus further comprises a windowprovided in the wall of the furnace through which the burner can beviewed.

Preferably, the window is made of quartz.

In one preferred embodiment, the interference filter could be providedas a panel attached to the sealed window of the furnace.

Still more preferably, the filter is a panel which can be placed overthe window or removed by a user as required. Thus for example, thefilter could be hinged to the wall of the furnace to allow quick andeasy adjustment thereof.

The provision of a panel over the window is considered to be novel andinventive in its own right and so, from a further aspect, the presentinvention provides a furnace comprising a burner housed within the wallsthereof and a window provided in a wall of the furnace, wherein aminterference filter adapted to pass light of only a narrow wavelengthrange is provided in or on the window.

In an alternative embodiment, the apparatus comprises a pair of glassesor goggles comprising an interference filter in each lens thereof.

The provision of such goggles is also considered to be novel andinventive in its own right and so, from a further aspect, the presentinvention provides glasses comprising an interference filter provided ineach lens thereof, wherein the interference filter is adapted to passlight of the wavelength of sodium only.

In another alternative embodiment of the invention, the apparatuscomprises a camera in which the interference filter is provided, whereinthe camera is arranged inside the furnace and adapted to photograph theburner at regular intervals. The information from the camera could thenbe relayed to an operator who could make any necessary adjustments tothe burner from a remote location.

Ideally the camera could be programmed to photograph the burner aboutonce every 10 minutes.

It will be appreciated that the furnace would normally include aplurality of burners and, in the case of a petroleum cracker, ten ormore burners could be provided. Thus if necessary, the camera could beprogrammed to move along a row of burners and to take pictures ofrespective burners or groups thereof.

Preferred embodiments of the invention will now be described, by way ofexample only, and with reference to the accompanying drawings in which:

FIG. 1 schematically shows a pyrolysis section of a petroleum cracker;and

FIG. 2 shows a pair of goggles according to one embodiment of theinvention.

As shown in FIG. 1, a petroleum cracker includes a pyrolysis section 1in which petroleum is heated in order to carry out the cracking process.The pyrolysis section includes a number of pipes or tubes 3 throughwhich the petroleum flows in use. Burners 5 are provided in the base 7of the pyrolysis section and further burners 9 are also provided in therear wall 11. The burners 5, 9 burn a mixture of hydrogen, air andmethane supplied to them by a pipe network (not shown).

The burners each produce a naked flame 13, the size and orientation ofwhich must be controlled in order to ensure even heating of thepetroleum pipes 3. In order to monitor the size and orientation of theflames 13, a window 15 made of quartz is provided in a wall of thepyrolysis section. The window is sealed so that the temperature andstability of the burner flames inside the pyrolysis section are notaffected by air currents from the window.

As shown in FIG. 2, goggles 17 are provided to be worn by a user whenviewing the flames 13. A sodium interference filter 19 is provided ineach lens of the goggles as shown. The sodium interference filters havea pass band of approximately 1 nm so that only light of wavelength 0.589μm passes through the filters. Thus, when a user wearing the gogglesviews the flames 13 of the burners 5, 9 through the window 15, onlylight from sodium trace elements in the burner flames is visible and theambient light from the walls of the pyrolysis section which glow whitehot is filtered out. Thus, the user can see the flames clearly and socan determine whether any adjustment to their size and/or orientation isrequired.

Any adjustments to the burner flames which are required are carried outby adjusting the quantity of fuel supplied to individual burners and/orthe ratio of air to fuel supplied to the burners and/or by adjusting thedirection of the jet of fuel emitted by the individual burners.

It will be appreciated that the embodiment of the invention describedabove is only a preferred embodiment thereof. Thus many variations couldbe made thereto without departing from the scope of the invention asclaimed. For example, the interference filters provided could have apass band of different wavelength, corresponding for example to thewavelength of another trace element in the burner flames. Further, theinterference filter could be provided in or on the window to the furnaceitself or in a camera arranged inside the furnace rather then in thegoggles described above.

It will therefore be appreciated that the above description is given byway of example only and is not intended to be limiting.

1. A method of viewing the flame produced by a burner in a furnace, wherein the fuel burnt by the burner is natural gas, comprising viewing the flame through an interference filter adapted to pass light of the wavelength of sodium only.
 2. A method as claimed in claim 1, wherein the furnace is the pyrolysis section of a petroleum cracker.
 3. A method as claimed in claim 1, wherein the fuel burnt by the burner is a mixture of hydrogen, methane and air.
 4. A method as claimed in claim 1, wherein a window is provided in the wall of the furnace through which the burner flame can be viewed.
 5. A method as claimed in claim 4, wherein the window is made of quartz.
 6. A method as claimed in claim 4, wherein the interference filter is provided as a panel attached to the window of the furnace.
 7. A method as claimed in claim 6, wherein the panel is hinged to the furnace so it can be placed over the window or removed by a user as required.
 8. A method as claimed in claim 1, wherein a pair of glasses or goggles having an interference filter in each lens thereof is provided.
 9. A method as claimed in claim 1, wherein the interference filter is provided in a camera arranged inside the furnace and adapted to photograph the burner at regular intervals.
 10. A method as claimed in claim 9, wherein the information from the camera is relayed to an operator who makes any necessary adjustments to the burner from a remote location.
 11. A method as claimed in claim 9, wherein the camera is programmed to photograph the burner about once every 10 minutes.
 12. A method as claimed in claim 9, wherein the camera is programmed to move along a row of burners and to photograph groups of one or more burner flames in turn.
 13. An apparatus comprising a furnace, a burner for burning natural gas in the furnace and an apparatus for viewing the flame produced by the burner, the apparatus for viewing the flame comprising an interference filter adapted to pass light of the wavelength of sodium only.
 14. An apparatus as claimed in claim 13, wherein a window is provided in the wall of the furnace through which the burner flame can be viewed.
 15. An apparatus as claimed in claim 14, wherein the window is made of quartz.
 16. An apparatus as claimed in claim 14, wherein the interference filter is provided as a panel attached to the window of the furnace.
 17. An apparatus as claimed in claim 14, wherein the filter is a panel which can be placed over the window or removed by a user as required.
 18. An apparatus as claimed in claim 13, wherein the apparatus for viewing the flame comprises a pair of glasses or goggles comprising an interference filter in each lens thereof.
 19. An apparatus as claimed in claim 13, wherein the apparatus for viewing the flame comprises a camera in which an interference filter is provided, wherein the camera is arranged inside the furnace and adapted to photograph the burner flame at regular intervals.
 20. An apparatus as claimed in claim 19, comprising means for relaying the information from the camera to an operator and means for making any necessary adjustments to the burner from a remote location.
 21. An apparatus as claimed in claim 19, wherein the camera is programmed to photograph the burner about once every 10 minutes.
 22. An apparatus as claimed in claim 19, wherein the camera is programmed to move along a row of burners and to photograph groups of one or more burner flames in turn.
 23. A furnace comprising a burner for burning natural gas housed within the walls thereof and a window provided in a wall of the furnace, wherein an interference filter adapted to pass light of the wavelength of sodium only is provided in or on the window.
 24. Glasses comprising an interference filter provided in each lens thereof, wherein the interference filter is adapted to pass light of the wavelength of sodium only. 